Which enzyme is responsible for removing an erroneous nucleotide in base excision repair?

In the context of base excision repair (BER), the key enzyme involved in identifying and removing an erroneous nucleotide is DNA glycosylase. This enzyme plays a critical role in the initial step of the repair process. It recognizes specific types of damaged or mispaired bases, such as those resulting from deamination or oxidation, and facilitates their removal by cleaving the glycosidic bond between the base and the sugar in the DNA backbone.

After DNA glycosylase removes the faulty base, an abasic site is created. This site is then repaired through further steps involving additional enzymes. DNA polymerase is subsequently recruited to synthesize the correct nucleotide to fill in the gap left by the removed base, and ligase seals the remaining nick in the sugar-phosphate backbone. Helicase, while important in other contexts of DNA repair and replication, does not play a direct role in the base excision step. Therefore, DNA glycosylase's specific function in base excision repair is crucial, making it the correct answer.